Study on coupled simulation of flow, temperature, and concentration in river reservoirs based on LB method

Abstract

[Objective] To address the complex hydrodynamic conditions in mountainous river reservoir systems, a three-dimensional flow-temperature-concentration coupled numerical model based on the lattice Boltzmann method is developed to describe water flow, thermal stratification, and pollutant transport processes. [Methods] A multi-distribution-function scheme was employed to solve the flow field, temperature field, and concentration field in parallel. The model was validated using three-dimensional double-diffusive natural convection cases, and the relative errors of the averaged Nusselt and Sherwood numbers under multiple Rayleigh number conditions were all less than 0.8%. On this basis, the model was applied to a typical river reservoir in the southwestern plateau to simulate water temperature evolution and short-term pollutant transport under cold-water inflow conditions. [Results] The result showed that after the cold-water inflow, a subsurface undercurrent formed at the reservoir bottom, inducing thermal stratification. When the main cold-water flow reached the dam site, downstream water temperature decreased from approximately 11.5 ℃ to approximately 6.5 ℃ within about 60 minutes. Pollutants accumulated locally in low-velocity zones, with high-concentration regions extending up to approximately 150 m, and were transported longitudinally in the mainstream predominantly by advection. [Conclusion] The coupled model can stably characterize the multi-field interactions of flow, temperature, and concentration under complex boundary conditions. It is applicable to high-resolution simulations of stratification induced by cold-water undercurrents and short-term pollutant transport in mountainous river reservoir systems, providing a reference for stratified water intake scheduling and pollution risk analysis.

Keywords

lattice Boltzmann method / multi-field coupling / river reservoir / heat and mass transfer / convection-diffusion / cold water inflow / stratified water withdrawal / pollution risk